SiC features a wide bandgap, and excellent chemical stability, electrical conductivity and heat conductivity. Power devices are extensively employed in various alternating-current to direct-current (AC/DC) conversion applications, and demand characteristics of low turn-on resistance, low leakage current, high breakdown voltage and fast switching in order to reduce turn-on loss and switching loss generated during operations. As SiC offers a high critical electric field of dielectric breakdown due to its wide bandgap, as well as an intrinsic carrier concentration far lower than doping concentrations in the devices, SiC power devices are suitable for high temperature, high frequency and high power applications.
For example, the U.S. Patent Publication No. US2006/0022292 discloses a structure, “Schottky Barrier Diode” (SBD). The structure features a substrate and two or more epitaxial layers. The epitaxial layers include at least a lightly doped n-type epitaxial layer, and another lightly doped n-type epitaxial layer having an even smaller doping concentration. Thus, by optimizing the thicknesses and doping concentrations of the two epitaxial layers, the capacitance and the switching loss of the SiC Schottky barrier diode is reduced, while maintaining a lower forward voltage drop and a lower turn-on resistance in the meantime.
The forward voltage drop of the Schottky barrier diode is mainly determined by the Schottky barrier which is determined by the work function of an anode metal layer and the electron affinity of SiC. A metal having a lower work function is generally selected for a lower Schottky barrier. However, the Schottky barrier would be further lowered due to the image force induced barrier lowering, which will result in a considerable leakage current at a reverse bias.